796 



A. S. Crafts 



2 4,0 



Amitrol 



Maleic Hydroride 



Fig. 5. Comparative mobility of 2,4-D (2,500 p.p.m.), amitrol (5,000 p.p.m.), and 

 maleic hydrazide (5,000 p.p.m.) in Zebrina pendula. Mature plants in depleted soil. 

 'J reatment 4 days with 0.5 jxc; top: radioautogram; bottom: mounted jjlants. 



movement when ihe treated j)lant is placed in a saturated atmos- 

 phere. Not only is phloem movement increased; there is apparently 

 a temporary reversal of the transpiration stream so that these com- 

 pounds are taken into the xylem and moved down into the stem and 

 then upward into untreated stem and leaves above the treated leaf. 

 Also the imtreated opposite cotyledon of cotton becomes labeled 

 when C^'*-labeled compounds are used. Figure 4 shows the results of 

 such treatments. 



One additional phenomenon needs consideration at this point; 

 this is the possible transfer of molecules from phloem to xylem dur- 

 ing their movement in the vascular channels. Figure 5 shows three 

 Zebrina plants treated with 2,4-D, amitrol, and MH, respectively. The 

 2,4-D has jjenctrated the cuticle, entered the symplast, moved to the 

 jihloem, and on inio adjacent stem tissue. However, because of bind- 

 ing in all living cells along the route it has moved only a few centi- 

 meters in llie slem. 



